OK, let's work through this together. We're starting with 91 and we're going to multiply it by 200, which means we add 91 to itself 200 times.
Step 1: 0 + 91 = 91
Step 2: 91 + 91 = 182
Step 3: 182 + 91 = 273
Step 4: 273 + 91 = 364
Step 5: 364 + 91 = 455
Step 6: 455 + 91 = 546
Step 7: 546 + 91 = 637
Step 8: 637 + 91 = 728
Step 9: 728 + 91 = 819
Step 10: 819 + 91 = 910
Step 11: 910 + 91 = 1001
Step 12: 1001 + 91 = 1092
Step 13: 1092 + 91 = 1183
Step 14: 1183 + 91 = 1274
Step 15: 1274 + 91 = 1365
Step 16: 1365 + 91 = 1456
Step 17: 1456 + 91 = 1547
Step 18: 1547 + 91 = 1638
Step 19: 1638 + 91 = 1729
Step 20: 1729 + 91 = 1820
Step 21: 1820 + 91 = 1911
Step 22: 1911 + 91 = 2002
Step 23: 2002 + 91 = 2093
Step 24: 2093 + 91 = 2184
Step 25: 2184 + 91 = 2275
Step 26: 2275 + 91 = 2366
Step 27: 2366 + 91 = 2457
Step 28: 2457 + 91 = 2548
Step 29: 2548 + 91 = 2639
Step 30: 2639 + 91 = 2730
Step 31: 2730 + 91 = 2821
Step 32: 2821 + 91 = 2912
Step 33: 2912 + 91 = 3003
Step 34: 3003 + 91 = 3094
Step 35: 3094 + 91 = 3185
Step 36: 3185 + 91 = 3276
Step 37: 3276 + 91 = 3367
Step 38: 3367 + 91 = 3458
Step 39: 3458 + 91 = 3549
Step 40: 3549 + 91 = 3640
Step 41: 3640 + 91 = 3731
Step 42: 3731 + 91 = 3822
Step 43: 3822 + 91 = 3913
Step 44: 3913 + 91 = 4004
Step 45: 4004 + 91 = 4095
Step 46: 4095 + 91 = 4186
Step 47: 4186 + 91 = 4277
Step 48: 4277 + 91 = 4368
Step 49: 4368 + 91 = 4459
Step 50: 4459 + 91 = 4550
Step 51: 4550 + 91 = 4641
Step 52: 4641 + 91 = 4732
Step 53: 4732 + 91 = 4823
Step 54: 4823 + 91 = 4914
Step 55: 4914 + 91 = 5005
Step 56: 5005 + 91 = 5096
Step 57: 5096 + 91 = 5187
Step 58: 5187 + 91 = 5278
Step 59: 5278 + 91 = 5369
Step 60: 5369 + 91 = 5460
Step 61: 5460 + 91 = 5551
Step 62: 5551 + 91 = 5642
Step 63: 5642 + 91 = 5733
Step 64: 5733 + 91 = 5824
Step 65: 5824 + 91 = 5915
Step 66: 5915 + 91 = 6006
Step 67: 6006 + 91 = 6097
Step 68: 6097 + 91 = 6188
Step 69: 6188 + 91 = 6279
Step 70: 6279 + 91 = 6370
Step 71: 6370 + 91 = 6461
Step 72: 6461 + 91 = 6552
Step 73: 6552 + 91 = 6643
Step 74: 6643 + 91 = 6734
Step 75: 6734 + 91 = 6825
Step 76: 6825 + 91 = 6916
Step 77: 6916 + 91 = 7007
Step 78: 7007 + 91 = 7098
Step 79: 7098 + 91 = 7189
Step 80: 7189 + 91 = 7280
Step 81: 7280 + 91 = 7371
Step 82: 7371 + 91 = 7462
Step 83: 7462 + 91 = 7553
Step 84: 7553 + 91 = 7644
Step 85: 7644 + 91 = 7735
Step 86: 7735 + 91 = 7826
Step 87: 7826 + 91 = 7917
Step 88: 7917 + 91 = 8008
Step 89: 8008 + 91 = 8099
Step 90: 8099 + 91 = 8190
Step 91: 8190 + 91 = 8281
Step 92: 8281 + 91 = 8372
Step 93: 8372 + 91 = 8463
Step 94: 8463 + 91 = 8554
Step 95: 8554 + 91 = 8645
Step 96: 8645 + 91 = 8736
Step 97: 8736 + 91 = 8827
Step 98: 8827 + 91 = 8918
Step 99: 8918 + 91 = 9009
Step 100: 9009 + 91 = 9100
Step 101: 9100 + 91 = 9191
Step 102: 9191 + 91 = 9282
Step 103: 9282 + 91 = 9373
Step 104: 9373 + 91 = 9464
Step 105: 9464 + 91 = 9555
Step 106: 9555 + 91 = 9646
Step 107: 9646 + 91 = 9737
Step 108: 9737 + 91 = 9828
Step 109: 9828 + 91 = 9919
Step 110: 9919 + 91 = 10010
Step 111: 10010 + 91 = 10101
Step 112: 10101 + 91 = 10192
Step 113: 10192 + 91 = 10283
Step 114: 10283 + 91 = 10374
Step 115: 10374 + 91 = 10465
Step 116: 10465 + 91 = 10556
Step 117: 10556 + 91 = 10647
Step 118: 10647 + 91 = 10738
Step 119: 10738 + 91 = 10829
Step 120: 10829 + 91 = 10920
Step 121: 10920 + 91 = 11011
Step 122: 11011 + 91 = 11102
Step 123: 11102 + 91 = 11193
Step 124: 11193 + 91 = 11284
Step 125: 11284 + 91 = 11375
Step 126: 11375 + 91 = 11466
Step 127: 11466 + 91 = 11557
Step 128: 11557 + 91 = 11648
Step 129: 11648 + 91 = 11739
Step 130: 11739 + 91 = 11830
Step 131: 11830 + 91 = 11921
Step 132: 11921 + 91 = 12012
Step 133: 12012 + 91 = 12103
Step 134: 12103 + 91 = 12194
Step 135: 12194 + 91 = 12285
Step 136: 12285 + 91 = 12376
Step 137: 12376 + 91 = 12467
Step 138: 12467 + 91 = 12558
Step 139: 12558 + 91 = 12649
Step 140: 12649 + 91 = 12740
Step 141: 12740 + 91 = 12831
Step 142: 12831 + 91 = 12922
Step 143: 12922 + 91 = 13013
Step 144: 13013 + 91 = 13104
Step 145: 13104 + 91 = 13195
Step 146: 13195 + 91 = 13286
Step 147: 13286 + 91 = 13377
Step 148: 13377 + 91 = 13468
Step 149: 13468 + 91 = 13559
Step 150: 13559 + 91 = 13650
Step 151: 13650 + 91 = 13741
Step 152: 13741 + 91 = 13832
Step 153: 13832 + 91 = 13923
Step 154: 13923 + 91 = 14014
Step 155: 14014 + 91 = 14105
Step 156: 14105 + 91 = 14196
Step 157: 14196 + 91 = 14287
Step 158: 14287 + 91 = 14378
Step 159: 14378 + 91 = 14469
Step 160: 14469 + 91 = 14560
Step 161: 14560 + 91 = 14651
Step 162: 14651 + 91 = 14742
Step 163: 14742 + 91 = 14833
Step 164: 14833 + 91 = 14924
Step 165: 14924 + 91 = 15015
Step 166: 15015 + 91 = 15106
Step 167: 15106 + 91 = 15197
Step 168: 15197 + 91 = 15288
Step 169: 15288 + 91 = 15379
Step 170: 15379 + 91 = 15470
Step 171: 15470 + 91 = 15561
Step 172: 15561 + 91 = 15652
Step 173: 15652 + 91 = 15743
Step 174: 15743 + 91 = 15834
Step 175: 15834 + 91 = 15925
Step 176: 15925 + 91 = 16016
Step 177: 16016 + 91 = 16107
Step 178: 16107 + 91 = 16198
Step 179: 16198 + 91 = 16289
Step 180: 16289 + 91 = 16380
Step 181: 16380 + 91 = 16471
Step 182: 16471 + 91 = 16562
Step 183: 16562 + 91 = 16653
Step 184: 16653 + 91 = 16744
Step 185: 16744 + 91 = 16835
Step 186: 16835 + 91 = 16926
Step 187: 16926 + 91 = 17017
Step 188: 17017 + 91 = 17108
Step 189: 17108 + 91 = 17199
Step 190: 17199 + 91 = 17290
Step 191: 17290 + 91 = 17381
Step 192: 17381 + 91 = 17472
Step 193: 17472 + 91 = 17563
Step 194: 17563 + 91 = 17654
Step 195: 17654 + 91 = 17745
Step 196: 17745 + 91 = 17836
Step 197: 17836 + 91 = 17927
Step 198: 17927 + 91 = 18018
Step 199: 18018 + 91 = 18109
Step 200: 18109 + 91 = 18200

So, 91*200 = 18200